Hydraulic Machinery

ABSTRACT

The invention addresses the problem of avoiding insufficient flow being supplied to the hydraulic actuator and speed becoming insufficient during light loads in hydraulic machinery such as hydraulic shovels when the engine rotation speed is set low during normal work. The solution is to increase the discharge flow of the hydraulic pump ( 2 ) by increasing the rotation speed of the engine ( 1 ) above the target rotation speed set by the engine rotation speed-setting means ( 14 ) when the hydraulic pump ( 2 ) discharge pressure is at the light load pump discharge pressure, the hydraulic pump ( 2 ) inclination angle is at the maximum inclination angle, and the negative control signal pressure is at the signal pressure when the hydraulic actuator-operating means ( 7 ) is at full operation.

TECHNICAL FIELD

The present invention relates to the technical field of a hydraulic workmachine such as a hydraulic shovel.

BACKGROUND ART

Generally, hydraulic work machines, such as hydraulic shovels, areconfigured to drive a hydraulic pump by an engine to operate varioushydraulic actuators (a hydraulic motor and a hydraulic cylinder) thatuse the hydraulic pump as a hydraulic pressure supply source, and thusperform various operations such as traveling and excavation. In recentyears, improvements in fuel efficiency and reductions of exhaust gasesin these hydraulic work machines have been in progress. One studiedmethod of achieving the objects is setting the engine rotation speed tobe low during normal operation. However, when the engine rotation speedis thus set to be low, the rotation speed of the hydraulic pump, drivenby the engine, is also lowered. Thus, the maximum flow rate that can besupplied from the hydraulic pump to the hydraulic actuator is reduced.As a result, a problem arises in that a sufficient speed cannot beobtained when the hydraulic actuator is to be operated at a high speedin a light load state.

A technique of controlling the engine rotation speed in accordance withthe load pressure to improve fuel efficiency in the light load state, isknown (see, for example, Patent Document 1). Here, when the load on thehydraulic actuator is light and the discharge pressure of the hydraulicpump is low, a desired discharge flow rate is obtained by lowering theengine rotation speed and increasing the capacity of the hydraulic pump.

Patent Document 1: Japanese Patent Application Laid-open No. H6-81802

DISCLOSURE OF THE INVENTION

However, when the engine rotation speed is set to be low during normaloperation, in an attempt to achieve lower fuel consumption, in thetechnique described in Patent Document 1 described above, the enginerotation speed, at the time when the load on the hydraulic actuator islight, is even lower than that during the normal operation. Thus, theflow rate from the hydraulic pump to the hydraulic actuator is notincreased with the increased capacity of the hydraulic pump. As aresult, the problem of the insufficient speed, when the hydraulicactuator is to be operated at a high speed in the light load state,cannot be solved. Thus, an object of the present invention is to solvethis problem.

With the foregoing in view, the present invention is made to solve theproblems and an invention of claim 1 is a hydraulic work machineincluding: an engine; a variable capacity hydraulic pump driven by theengine; a hydraulic actuator that operates using the hydraulic pump as ahydraulic pressure supply source; a control valve that is displaced inaccordance with an operation amount of a hydraulic actuator operationmeans so as to control a pressure oil supply flow rate from thehydraulic pump to the hydraulic actuator; a negative control circuitthat outputs a negative control signal pressure to capacity varyingmeans of the hydraulic pump to increase or decrease a discharge flowrate of the hydraulic pump in accordance with a displacement amount ofthe control valve; an engine rotation speed setting means operated toset a target rotation speed of the engine; and an engine control devicethat controls a rotation speed of the engine based on the targetrotation speed set with the engine rotation speed setting means. Thehydraulic work machine further includes pump pressure detection meansfor detecting a discharge pressure of the hydraulic pump, pump capacitydetection means for detecting a capacity of the hydraulic pump, andnegative control signal pressure detection means for detecting thenegative control signal pressure. The engine control device performsengine rotation speed increasing control for increasing the enginerotation speed to be higher than the target rotation speed set with theengine rotation speed setting means, when the discharge pressure of thehydraulic pump detected by the pump pressure detection means is notlarger than a set pump pressure set in advance as a pump dischargepressure in a light load state, the pump capacity detected by the pumpcapacity detection means is at a maximum capacity of the hydraulic pump,and the negative control signal pressure detected by the negativecontrol signal pressure detection means is not larger than a set signalpressure set in advance as a negative control signal pressure in a fullyoperated state of the hydraulic actuator operation means .

With the invention of claim 1, even in the case where the enginerotation speed is set to be low during normal operation to achieve lowerfuel consumption, the engine rotation speed increases when the enginerotation speed increasing control is performed, and thus the dischargeflow rate of the hydraulic pump can be increased. This can preventinsufficient speed due to an insufficient supply flow rate to thehydraulic actuator in the case where an operation requiring high speedat a light load is performed, whereby excellent operability isguaranteed and an attempt to improve work efficiency is largelyfacilitated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a hydraulic pressure control circuit diagram of a hydraulicshovel.

FIG. 2 is a flowchart of engine rotation speed control.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention is described below by referringto the drawings.

A hydraulic pressure control circuit provided to a hydraulic shovel, asan example of a hydraulic work machine, is illustrated in FIG. 1, inwhich 1 denotes an engine, 2 denotes a variable capacity hydraulic pumpdriven by the engine 1, 2 a denotes capacity varying means of thehydraulic pump 2, 3 denotes an oil tank, and A denotes hydraulicactuators that operate using the hydraulic pump 2 as a hydraulicpressure supply source. In this embodiment, the hydraulic shovelincludes, as the hydraulic actuators A, left and right drive motors, aswing motor, a boom cylinder, an arm cylinder, and a bucket cylinder. Inthis embodiment, an axial piston pump, in which a capacity changes inaccordance with a inclination angle of a swash plate, is used as thehydraulic pump 2.

Furthermore, 4 denotes control valves that perform oil supply/dischargecontrol for the respective hydraulic actuators A. The control valve 4 isconfigured to be positioned at a neutral position N in which pressureoil is not supplied to the hydraulic actuator A, in a state where nopilot pressure is supplied to pilot ports 4 a and 4 b, and is configuredto be displaced when the pilot pressure is supplied to the pilot ports 4a and 4 b and to be switched to an operation position X or Y in which adischarged oil from the hydraulic pump 2 is supplied to the hydraulicactuator A. Here, a control is performed in such a manner that thedisplacement amount (movement stroke) of the control valve 4increases/decreases in accordance with the increase/decrease of thepilot pressure input to the pilot ports 4 a and 4 b, and a pressure oilsupply flow rate to the hydraulic actuator A increases when adisplacement amount of the control valve 4 increases. A center bypassvalve path 4 c to be connected to a center bypass oil path 5, describedlater, is formed in each control valve 4. The opening amount of thecenter bypass valve path 4 c is at the maximum when the control valve 4is at the neutral position N, and reduces as the displacement amount ofthe control valve 4 increases.

Furthermore, 6 denotes a pilot valve. The pilot valve 6 outputs thepilot pressure to each of the pilot ports 4 a and 4 b of the controlvalve 4, based on an operation on a hydraulic actuator operation device(operation devices respectively for left and right traveling, swing, theboom, the arm, and the bucket, in this embodiment) 7. Here, the pilotpressure output from the pilot valve 6 increases/decreases in accordancewith the operation amount on the hydraulic actuator operation means 7.In FIG. 1, only the pilot valve 6 that outputs the pilot pressure to thecontrol valve 4 at the right end is illustrated, and the pilot valves 6that output the pilot pressure to other control valves 4 are omittedbecause the pilot valves are the same as the right end one.

The center bypass oil path 5 is an oil path that is formed to extendfrom the hydraulic pump 2, sequentially pass through the center bypassvalve paths 4 c formed in the respective control valves 4, and then passthrough a negative control orifice 8 to reach the oil tank 3. Thepressure on the upstream side of the negative control orifice 8 in thecenter bypass oil path 5 is input, as a negative control signalpressure, to the capacity varying means 2 a of the hydraulic pump 2,through a signal circuit 9. The negative control signal pressure is highwhen the opening amount of the center bypass valve path 4 c of thecontrol valve 4 is maximum, that is, when the control valve 4 ispositioned at the neutral position N, while the negative control signalpressure becomes lower as the opening amount of the center bypass valvepath 4 c becomes smaller, that is, as the displacement amount of thecontrol valve 4 becomes larger. The capacity varying means 2 a of thehydraulic pump 2 controls the discharge flow rate of the hydraulic pump2, in such a manner that the negative control signal pressure at ahigher pressure leads to a smaller discharge flow rate of the hydraulicpump 2, and the negative control signal pressure at a lower pressureleads to a larger discharge flow rate of the hydraulic pump 2. Thecenter bypass valve path 4 c of the control valve 4, the center bypassoil path 5, the negative control orifice 8, and the signal circuit 9form a negative control circuit of the present invention.

Furthermore, 10 denotes an engine control device that controls therotation speed of the engine 1. The engine control device 10 receives asignal from each of a pump pressure detection sensor (corresponding topump pressure detection means of the present invention) 11 that detectsthe discharge pressure of the hydraulic pump 2, a inclination angledetection sensor (corresponding to pump capacity detection means of thepresent invention) 12 that detects the inclination angle of the swashplate of the hydraulic pump 2, a negative control signal pressuredetection sensor (corresponding to negative control signal pressuredetection means of the present invention) 13 that detects the negativecontrol signal pressure, and an engine rotation speed setting means(such as an accelerator dial and an accelerator lever) 14. The enginecontrol device 10 controls the rotation speed of the engine 1, based onthe input signals.

Here, the engine rotation speed setting means 14 is an operation meansused by an operator to set the target rotation speed of the engine 1 asdesired. In this embodiment, the operator can set the engine rotationspeed to a plurality of levels by using the engine rotation speedsetting means 14. The engine rotation speed setting means 14 may enablethe engine rotation speed to be set in a stepless manner.

Next, an engine rotation speed control performed by the engine controldevice 10 will be described by referring to the flowchart in FIG. 2.

First, the engine control device 10 receives signals from the pumppressure detection sensor 11, the inclination angle detection sensor 12,a negative control signal pressure detection sensor 13, and the enginerotation speed setting means 14 (step S1).

Then, the engine control device 10 determines whether a negative controlsignal pressure Pn, detected by the negative control signal pressuredetection sensor 13, is not larger than a set signal pressure PnS (1.8Mpa, for example) (Pn≦PnS?), the set signal pressure Pns being set inadvance as a negative control signal pressure when at least onehydraulic actuator operation means 7 is in a fully operated state (atleast one control valve 4 is displaced by the maximum displacementamount) (step S2).

When “YES” is determined in step S2 described above, that is, when thenegative control signal pressure Pn is not larger than the set signalpressure PnS (Pn≦PnS), it is further determined whether the dischargepressure Pp of the hydraulic pump 2 detected by the pump pressuredetection sensor 11 is not larger than a set pump pressure PpS (20 MPafor example) (Pp≦PpS?), the set pump pressure PpS being set in advanceas a pump discharge pressure in the light load state (step S3).

When “YES” is determined in step S3 described above, that is, when thedischarge pressure Pp of the hydraulic pump 2 is not larger than the setpump pressure PpS (Pp≦PpS), whether the inclination angle Sθ of theswash plate of the hydraulic pump 2, detected by the inclination angledetection sensor 12, is at the maximum inclination angle SOm at whichthe capacity of the hydraulic pump 2 (Sθ=Sθm?) is maximum, is furtherdetermined (step S4).

When “YES” is determined in step S4 described above, that is, when theinclination angle Sθ of the swash plate of the hydraulic pump 2 is atthe maximum inclination angle Sθm (Sθ=Sθm) , the engine control device10 performs an engine rotation speed increasing control for increasingthe engine rotation speed up to a light-load state rotation speed thatis higher than the target rotation speed set with the engine rotationspeed setting means 14 (step S5). Here, the light-load state rotationspeed is higher than the target rotation speed set with the enginerotation speed setting means 14, by a predetermined rotation speed (200rps, for example), and is set for each target rotation speed.

The engine rotation speed increasing control for increasing the enginerotation speed up to the light-load state rotation speed that is higherthan the target rotation speed set with the engine rotation speedsetting means 14 is performed, when “YES” is determined in all of stepsS2, S3, and S4 described above, that is, when the negative controlsignal pressure Pn is not larger than the set signal pressure PnS (thehydraulic actuator operation means 7 is in the fully operated state),the discharge pressure Pp of the hydraulic pump 2 is not larger than theset pump pressure PpS (in the light load state), and the inclinationangle Sθ of the swash plate of the hydraulic pump 2 is at the maximuminclination angle Sθm (the capacity of the hydraulic pump 2 is at themaximum). Thus, the rotation speed of the hydraulic pump 2, driven bythe engine 1, is increased by performing the engine rotation speedincreasing control, whereby the discharge flow rate of the hydraulicpump 2 can be increased.

On the other hand, when “NO” is determined in any one of steps S2, S3,and S4 described above, that is, when the negative control signalpressure exceeds the set signal pressure (Pn>PnS), when the dischargepressure of the hydraulic pump 2 exceeds the set pump pressure (Pp>PpS),or when the inclination angle of the swash plate of the hydraulic pump 2is not at the maximum inclination angle (Sθ≠Sθm), the engine controldevice 10 controls the engine rotation speed so that the target rotationspeed set with the engine rotation speed setting means 14 is achieved(step S6).

In this embodiment configured as described above, the hydraulic shovelincludes: the engine 1; the variable capacity hydraulic pump 2 driven bythe engine 1; the hydraulic actuator A that operates using the hydraulicpump 2 as a hydraulic pressure supply source; the control valve 4 thatis displaced in accordance with an operation amount of a hydraulicactuator operation means 7 so as to control a pressure oil supply flowrate from the hydraulic pump 2 to the hydraulic actuator A; the negativecontrol circuit (the center bypass valve path 4 c of the control valve4, the center bypass oil path 5, the negative control orifice 8, and thesignal circuit 9) that outputs the negative control signal pressure tothe capacity varying means 2 a of the hydraulic pump 2 to increase ordecrease a discharge flow rate of the hydraulic pump 2 in accordancewith a displacement amount of the control valve 4; the engine rotationspeed setting means 14 operated to set the target rotation speed of theengine 1; and the engine control device 10 that controls a rotationspeed of the engine 1 based on the target rotation speed set with theengine rotation speed setting means 14. The hydraulic shovel furtherincludes the pump pressure detection sensor 11 for detecting a dischargepressure of the hydraulic pump 2, the inclination angle detection sensor12 for detecting the inclination angle of the hydraulic pump 2, and thenegative control signal pressure detection sensor 13 for detecting thenegative control signal pressure. The engine control device 10 performsengine rotation speed increasing control for increasing the rotationspeed of the engine 1 up to the light-load state rotation speed higherthan the target rotation speed set with the engine rotation speedsetting means 14, when the discharge pressure of the hydraulic pump 2detected by the pump pressure detection sensor 11 is not larger than aset pump pressure set in advance as a pump discharge pressure in thelight load state, the inclination angle of the swash plate of thehydraulic pump 2 detected by the inclination angle detection sensor 12is at the maximum inclination angle (the pump capacity is at the maximumcapacity), and the negative control signal pressure detected by thenegative control signal pressure detection sensor 13 is not larger thanthe set signal pressure set in advance as the negative control signalpressure in the fully operated state of the hydraulic actuator operationmeans 7.

When, in the light load state, the capacity of the hydraulic pump 2 isat the maximum capacity, and the hydraulic actuator operation means 7 isin the fully operated state, the engine rotation speed increasingcontrol is performed for increasing the engine rotation speed up to thelight-load state rotation speed higher than the target rotation speedset with the engine rotation speed setting means 14. Thus, the rotationspeed of the hydraulic pump 2 also increases. As a result, by setting alow target rotation speed with the engine rotation speed setting means14 and performing an operation with the low target rotation speed duringnormal operation, a lower fuel consumption can be achieved, and thedischarge flow rate of the hydraulic pump 2 can be increased by theengine rotation speed increasing control in the light load state. Thus,for example, when an operation such as dumping or return operationduring truck loading, requiring a high speed with a light load, isperformed, an insufficient speed due to an insufficient supply flow rateto the hydraulic actuator A can be prevented, whereby an excellentoperability is guaranteed, and an attempt to improve the work efficiencyis largely facilitated.

INDUSTRIAL APPLICABILITY

The present invention can be used for various hydraulic work machinessuch as a hydraulic shovel, including a hydraulic pump driven by anengine and a hydraulic actuator that operates using the hydraulic pumpas a hydraulic pressure supply source.

EXPLANATION OF REFERENCE NUMERALS

-   1 Engine-   2 Hydraulic pump-   4 Control valve-   4 c Center bypass valve path-   5 Center bypass oil path-   7 Hydraulic actuator operation means-   8 Negative control orifice-   9 Signal circuit-   10 Engine control device-   11 Pump pressure detection sensor-   12 Inclination angle detection sensor-   13 Negative control signal pressure detection sensor-   14 Engine rotation speed setting means

1. A hydraulic machine comprising: an engine; a variable capacityhydraulic pump driven by the engine, and having a capacity and operableas a hydraulic pressure supply source; an adjustable control coupled tothe hydraulic pump, the adjustable control disposed to vary the capacityof the hydraulic pump; a hydraulic actuator fluidly coupled to andoperable by the hydraulic pump; a control valve fluidly disposed betweenthe hydraulic pump and the hydraulic actuator that is adapted to bedisplaced a displacement amount in accordance with an operation amountof an operator actuator control so as to control a pressure oil supplyflow rate from the hydraulic pump to the hydraulic actuator; a negativecontrol circuit that outputs a negative control signal pressure to theadjustable control to increase or decrease a discharge flow rate of thehydraulic pump in accordance with the displacement amount of the controlvalve; an engine rotation speed control operable to set a targetrotation speed of the engine; and an engine control device that controlsa rotation speed of the engine based on the target rotation speed setwith the engine rotation speed control; a pump pressure detection sensordisposed and adapted to detect a discharge pressure of the hydraulicpump; a pump capacity detection sensor disposed and adapted to detectthe capacity of the hydraulic pump; and a negative control signalpressure detection sensor disposed and adapted to detect the negativecontrol signal pressure, wherein the engine control device is adapted toincrease the engine rotation speed to be higher than the target rotationspeed set with the engine rotation speed control, when the dischargepressure of the hydraulic pump detected by the pump pressure detectionsensor means is not larger than a preset pump discharge pressure in alight load state, the pump capacity detected by the pump capacitydetection sensor means is at a maximum capacity of the hydraulic pump,and the negative control signal pressure detected by the negativecontrol signal pressure detection sensor is not larger than a presetnegative control signal pressure in a fully operated state of theoperator actuator control.
 2. The machine as claimed in claim 1 whereinthe hydraulic actuator includes at least one of a drive motor, a swingmotor, and a cylinder.
 3. A method of controlling a hydraulic circuitincluding providing to an engine control device a signal indicative ofpump discharge pressure, providing to the engine control device a signalindicative of an inclination angle of an adjustable swashplateassociated with a variable capacity hydraulic pump, providing to theengine control device a signal indicative of a negative controlpressure, providing to the engine control device a signal indicative ofa setting of a rotation speed of an engine disposed to drive thehydraulic pump, determining whether the negative control signal pressureis not larger than a preset signal pressure, determining whether thepump discharge pressure is not larger than a preset pump pressure,determining whether the inclination angle of the adjustable swashplateis at a maximum inclination angle at which the capacity of the hydraulicpump is at a maximum, if the negative control signal pressure is notlarger than the preset signal pressure, if the pump discharge pressureis not larger than the preset pump pressure, and if the inclinationangle is at the maximum inclination angle, then performing an enginerotation speed increasing control to increase the engine rotation speedup to a light-load state rotation speed higher than a target rotationspeed set by an engine rotation speed control.
 4. The method of claim 3further including controlling the engine rotation speed to achieve thetarget rotation speed set with the engine rotation speed control if anyof the following is determined: the negative control signal pressure islarger than the preset signal pressure, the pump discharge pressure islarger than the preset pump pressure, and the inclination angle is notat the maximum inclination angle.
 5. The method of claim 3 whereinproviding a signal indicative of pump discharge pressure includessensing pressure within the variable capacity hydraulic pump.
 6. Themethod of claim 3 wherein providing a signal indicative of theinclination angle includes sensing the inclination angle of theadjustable swashplate associated with the pump,
 7. The method of claim 3wherein providing a signal indicative of a setting of a rotation speedof an engine disposed to drive the hydraulic pump includes determiningthe position of an engine rotation speed control.
 8. The method of claim3 wherein providing a signal indicative of a negative control pressureincludes sensing the negative control signal pressure.
 9. The method ofclaim 3 further including setting the preset signal pressure based upona negative control signal pressure when at least one operator actuatorcontrol is in a fully operated state.
 10. The method of claim 9 whereinthe fully operated state is when at least one control valve is displacedby a maximum displacement amount.
 11. The method of claim 3 furtherincluding setting the preset pump pressure as a pump discharge pressurein a light load state.
 12. The method of claim 3 wherein the light-loadstate rotation speed is higher than the target rotation speed set withthe engine rotation speed control by a predetermined rotation speed. 13.The method of claim 12 wherein the predetermined rotation speed is setfor each target rotation speed.
 14. The method of claim 4 whereinproviding a signal indicative of pump discharge pressure includessensing pressure within the variable capacity hydraulic pump.
 15. Themethod of claim 4 wherein providing a signal indicative of theinclination angle includes sensing the inclination angle of theadjustable swashplate associated with the pump.
 16. The method of claim4 wherein providing a signal indicative of a setting of a rotation speedof an engine disposed to drive the hydraulic pump includes determiningthe position of an engine rotation speed control.
 17. The method ofclaim 4 wherein providing a signal indicative of a negative controlpressure includes sensing the negative control signal pressure.
 18. Themethod of claim 4 further including setting the preset signal pressurebased upon a negative control signal pressure when at least one operatoractuator control is in a fully operated state.
 19. The method of claim 4further including setting the preset pump pressure as a pump dischargepressure in a light load state.
 20. The method of claim 4 furtherincluding setting the preset signal pressure based upon a negativecontrol signal pressure when at least one operator actuator control isin a fully operated state, and setting the preset pump pressure as apump discharge pressure in a light load state, and wherein providing asignal indicative of pump discharge pressure includes sensing pressurewithin the variable capacity hydraulic pump, providing a signalindicative of the inclination angle includes sensing the inclinationangle of the adjustable swashplate associated with the pump, providing asignal indicative of a setting of a rotation speed of an engine disposedto drive the hydraulic pump includes determining the position of anengine rotation speed control, and providing a signal indicative of anegative control pressure includes sensing the negative control signalpressure.